The first trimester is the early stage of pregnancy, lasting up to 13 weeks. It is a crucial period as it marks the beginning of your baby's growth and brings many changes to your body. Due to the changes and symptoms you might experience, it can be an exciting time filled with joy and sometimes a bit of worry. Understanding what happens during these first 13 weeks, from how your baby develops to the changes in your body and feelings, is essential. This guide will help explain everything you need to know about the first trimester, providing tips to handle the new changes and care for yourself and your baby during this critical time.

Medically Reviewed by:

Senior Consultant, ART Fertility Clinics India
Pregnancy is classified into three stages called trimesters. The first trimester is the initial stage, which lasts until the end of the 13th week. Although it might seem strange, pregnancy is calculated from the first day of your last menstrual period. This means by the time you realize you’re pregnant, you might already be around four weeks along.
During the first trimester of pregnancy, the initial stages of fetal development occur, starting with fertilization and continuing through the formation of critical organs and structures. Here is a closer look at what happens week by week:
Weeks 1 to 4:
The journey begins with your last menstrual period, week one. By the end of week 4, fertilization (the meeting of sperm and egg) has likely occurred, leading to the creation of an embryo. This tiny new life is smaller than a grain of rice.
Weeks 5 to 8:
Major changes start here. By week 6, critical organs like the heart begin to form, and by the end of week 8, the embryo will have a more human shape, with the beginning of arms, legs, eyes, and ears. The embryo at this stage is about an inch long, roughly the size of a raspberry.
Weeks 9 to 12:
The development continues rapidly. The fetus starts to move a little, even though you won’t feel it yet. The organs continue to develop, and by the end of week 12, the fetus is about two to three inches long, about the size of a plum, and weighs roughly an ounce.
During the first trimester, your body undergoes significant changes to support the growing fetus. Here are some of the changes you might notice:
It is not just your body that changes—your emotions might also be everywhere. You might feel joyous one moment and anxious the next. These mood swings are normal and are primarily due to hormonal changes.
During the first trimester of pregnancy, taking good care of your health is essential for you and your baby’s development. Here are some important steps and tips to ensure a healthy start to your pregnancy journey:
During your first trimester, you’ll have your initial prenatal visit, where your healthcare provider will do several tests:
The first trimester is a critical and exciting period in your pregnancy. Understanding what to expect and how to care for yourself and your baby during these early weeks can help you manage the changes more effectively.
Every pregnancy is unique, so you must communicate with your healthcare provider about any concerns or symptoms. Enjoy this time as you start the incredible journey of bringing a new life.